Oligohydramnios

Roya Sohaey, MD

DIFFERENTIAL DIAGNOSIS

Common

Preterm Premature Rupture of Membranes (PPROM)
Intrauterine Growth Restriction (IUGR)
Bilateral Renal Anomaly
- Renal Agenesis
- Ureteropelvic Junction Obstruction (UPJ)
- Multicystic Dysplastic Kidney (MCDK)
- Autosomal Recessive Polycystic Kidney Disease
Bladder Outlet Obstruction
- Posterior Urethral Valves
- Urethral Atresia

Less Common

Twin-Twin Transfusion Syndrome

Rare but Important

Prune Belly Syndrome

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Diagnosis of oligohydramnios
- Subjective
  - ↓ Pockets of fluid
  - Fetus:fluid ratio > 1:1
- Objective
  - Maximum vertical pocket is ↓ 2 cm
  - Amniotic fluid index < 5 cm

Helpful Clues for Common Diagnoses

Preterm Premature Rupture of Membranes (PPROM)
- Clinical diagnosis
- Etiology
  - Spontaneous
  - Infection
  - Post-amniocentesis
- Worse prognosis if PPROM early or prolonged
  - Early: PPROM < 25 weeks
  - Prolonged: PPROM > 14 days
Intrauterine Growth Restriction (IUGR)
- Estimated fetal weight < 10th percentile
- Oligohydramnios often earliest finding
- Causes
  - Placental insufficiency
  - Fetal aneuploidy/syndrome
- Doppler assessment
  - ↑ Umbilical artery resistance
  - ↑ Uterine artery resistance
  - ↓ Middle cerebral artery resistance
Renal Agenesis
- Ultrasound findings
  - Anhydramnios (no fluid)
  - Absent kidneys and bladder
  - No renal arteries (color Doppler)
  - Clubfeet, other joint contractures
- Pitfalls
  - May have normal fluid early (< 17 weeks)
  - Bladder secretions may mimic urine
  - Adrenal gland may mimic kidney
  - Bowel in renal fossa may mimic kidney
- Fatal prognosis
  - Pulmonary hypoplasia
Ureteropelvic Junction Obstruction (UPJ)
- Ultrasound findings
  - ↑ Renal pelvis is hallmark finding
  - Renal pelvis ≥ 7 mm after 33 weeks
  - Associated caliectasis
  - No distended ureter or bladder
- Evaluate contralateral kidney
  - Bilateral UPJ in 10%
  - UPJ + contralateral renal anomaly in 25%
- Prognosis
  - Depends on severity of obstruction
  - Early oligohydramnios pulmonary hypoplasia
  - Post-obstructive cystic dysplasia
Multicystic Dysplastic Kidney (MCDK)
- Renal tissue replaced by cysts
- Ultrasound findings
  - Multiple variable-sized cysts
  - Kidney may lose reniform shape
  - ↑ Renal size initially, then ↓
  - Severe oligohydramnios if bilateral
- 20% of MCDK are bilateral (anhydramnios)
- 40% have contralateral renal anomaly
- Poor prognosis if bilateral anomalies
Autosomal Recessive Polycystic Kidney Disease
- Single gene disorder
  - Distal tubule/collecting duct dilatation
- Ultrasound findings
  - Enlarging echogenic kidneys
  - Majority detected > 24 weeks
  - Macrocysts rarely seen
  - Variable oligohydramnios
- Perinatal, neonatal, infantile and juvenile presentations
  - Perinatal form with 30-50% mortality
  - Severe oligohydramnios pulmonary hypoplasia
  - Hepatic fibrosis (rarely in utero)
Posterior Urethral Valves
- Partial or complete obstruction
- “Keyhole” appearance
  - ↑ Bladder + ↑ posterior urethra
- Variable hydronephrosis/hydroureter
  - ± Post-obstructive renal cystic dysplasia
- Spontaneous decompression may occur
  - Bladder rupture urinary ascites
  - Renal fornix rupture urinoma
- In-utero treatment if severe oligohydramnios
  - Serial bladder drainage
  - Vesicoamniotic shunt
- In female fetuses, consider urethral atresia